Methods and apparatus for additive manufacturing utilizing multifunctional composite materials, and articles made therefrom

ABSTRACT

A method of depositing a multiphase material. The method includes providing a Continuous Multifunctional Composite (CMC) phase containing at least one continuous element in a polymeric matrix, passing the CMC phase through a feeding system containing a cutting system, producing a predetermined length of the CMC phase, providing a flow a molten polymer such that the molten polymer and the CMC phase are merged into a continuous co-extrusion nozzle so as to produce a co-extruded multiphase material, and depositing the co-extruded multiphase material onto a surface. An apparatus for depositing a multiphase material. The apparatus contains a co-extrusion nozzle, a means to introduce a CMC phase and a molten polymer into the co-extrusion nozzle, such that the molten polymer and the CMC phase are co-extruded and deposited on a surface. An article containing a CMC phase containing continuous elements embedded in a polymer resin forming a multiphase structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. patent application is related to and claims thepriority benefit of U.S. Provisional Patent Application Ser. No.62/658,366 filed Apr. 16, 2018, the contents of which are herebyincorporated by reference in their entirety into the present disclosure.

STATEMENT REGARDING GOVERNMENT FUNDING

This invention was made with government support under DE-EE0006926awarded by the Department of Energy. The government has certain rightsin the invention.

TECHNICAL FIELD

This disclosure relates to additive manufacturing methods and apparatusand especially to methods and apparatus for additive manufacturing ofarticles by co-extruding continuous multifunctional composite materials,and articles made using such methods and apparatus.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

The technology of Extrusion Deposition Additive Manufacturing (EDAM)involves manufacturing three-dimensional geometries by depositing beadsof molten material in a layer-by-layer basis. EDAM is a screwextruder-based process that has enabled processing high-temperature andhighly reinforced polymer composites that otherwise could not beprocessed with traditional filament-based processes due to the highviscosity of the reinforced polymer. Further, printing structures of thelarge-scale size (meters) has become feasible due to advancements in theprinting materials and the EDAM technology, Specific advancementsinclude the reduction in coefficient of thermal expansion (CTE) and theincrease in stiffness gained along the print direction by reinforcingprinting polymers with discontinuous fibers as described in literature.Previous work has focused on printing with carbon fiber reinforcedPolyphenylene Sulfide (PPS), which is a semi-crystallinehigh-temperature polymer processed at 310° C. Examples of commerciallyavailable extrusion deposition additive systems are the LSAM® developedby Thermwood® and the BAAM® developed by Cincinnati Inc®.

The EDAM process of polymer composites utilizes pelletized compositematerial that contains discontinuous fibers impregnated with polymer.The pelletized material can take the form of Long Discontinuous Fiber(LDF) or compounded composite with the primary difference in the initialfiber length where LDF lengths are in the range of 10,000 microns,whereas fiber length in compounded material is typically below 500microns. The pelletized material is fed into a single-screw extrusionsystem that melts and applies pressure to the printing material. Twoprimary sources of heat drive the melting process of the polymer in ascrew-based extrusion system. The first one is the heat suppliedexternally from heaters and the second is the viscous dissipation (shearheating) in the polymer. This mechanism requires substantial mechanicalenergy that results in fiber fracture and thereby, fiber lengthattrition. After flowing through the extruder, the molten polymercomposite enters the printing nozzle where converging zones cause thefibers to orient in the print direction, thereby introducing anisotropyin the mechanical, thermal and flow properties of the extrudate. In thecontext of this disclosure, the term “extrudate” refers to the physicalentity resulting from an extrusion process or a co-extrusion process.Co-extrusion refers to extrusion of more than one material or phasetogether to form a physical entity. Upon leaving the nozzle, thecomposite material is first deposited on an actively heated build plateand in subsequent passes it is deposited on previously depositedmaterial substrate layers. Finally, the deposited extrudate isconsolidated with a compaction mechanism in order to reduce extrudatethickness and to consolidate the extrudate with adjacent depositedlayers.

Fiber attrition in the extrusion process of the polymer compositeadditive manufacturing is one of the factors limiting the strength in aprinted component. Therefore, current applications for EDAM withcomposites has been limited to non-structural applications

Hence, there exists an unmet need for methods and apparatus for additivemanufacturing of polymer composites by extrusion without reducing orlimiting the strength of a printed component or article.

SUMMARY

A method of depositing a multiphase material is disclosed. The methodincludes providing a CMC phase containing at least one continuouselement comprising at least one material impregnated in a polymericmatrix, passing the CMC phase containing the at least one continuouselement through a feeding system containing a cutting system, producinga predetermined length of the CMC phase containing at least onecontinuous element by activating the cutting system, providing a flow amolten polymer such that the molten polymer and the CMC phase containingat least one continuous element of predetermined length are merged intoa continuous co-extrusion nozzle so as to produce a co-extrudedmultiphase material, and depositing the co-extruded multiphase materialonto a surface.

An apparatus for depositing a multiphase material is disclosed. Theapparatus contains a feedings system capable of continuously feeding aCMC phase containing continuous elements, and containing a cuttingsystem capable of producing a predetermined length of the CMC phasecontaining continuous elements; a co-extrusion nozzle comprising a flowchannel; a means to introduce the predetermined length of the CMC phasecontaining continuous elements into the flow channel of the co-extrusionnozzle; and a means to introduce a molten polymer into the flow channelsuch that the molten polymer and the predetermined length of the CMCphase containing continuous elements are co-extruded and deposited on asurface.

An article containing a CMC phase containing continuous elementsembedded in a polymer resin forming a multiphase structure is disclosed.

BRIEF DESCRIPTION OF DRAWINGS

Some of the figures shown herein may include dimensions. Further, someof the figures shown herein may have been created from scaled drawingsor from photographs that are scalable. It is understood that suchdimensions or the relative scaling within a figure are by way ofexample, and not to be construed as limiting.

FIG. 1 shows the steady state temperature distribution in the multiphasematerial system co-extruded at different speeds.

FIG. 2 shows the steady state distribution of crystallinity in themultiphase material system co-extruded at different speeds.

FIG. 3 shows a schematic illustration of the co-extrusion system orapparatus of this disclosure for printing with two phases (CMC phase andphase in the molten state)

FIG. 4A shows a cross-sectional view of the co-extrusion apparatus 4000of this disclosure with greater detail of several of its constituentparts.

FIG. 4B shows a simplified cross-sectional view of the co-extrusionsystem or apparatus of this disclosure.

FIG. 5 shows an exemplary representation of a geometry capable of beingfabricated by the apparatus of FIG. 4A and methods of this disclosure.

FIG. 6 shows the cross-sectional view of an exemplary article printedwith a CMC phase using the methods and apparatus of this disclosure.

FIG. 7A shows the microstructure of a CMC phase made with continuouscarbon fiber (shown in white) impregnated with PPS (shown in grey).

FIG. 7B shows a magnified view of the microstructure of a CMC phase madewith continuous carbon fiber (shown in white) impregnated with PPS(shown in grey).

FIG. 8 shows a representative volume element of a multiphase materialsystem utilized in the finite element analysis used in this disclosure.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thedisclosure, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of thedisclosure is thereby intended.

This disclosure describes methods and apparatus to continuously and/orselectively print with material systems containing at least two phases.One phase can contain unreinforced polymeric material or polymericmaterial reinforced with fillers. Examples of such fillers used forreinforcing include, but are not limited to, organic fillers, mineralfillers, discontinuous fibers made of carbon, glass, aramid, or naturalfibers such as jute. This phase containing unreinforced polymericmaterial or polymeric material reinforced with fillers is called adiscontinuous phase in this disclosure. A second phase can containcontinuous elements impregnated with a polymeric matrix. Thesecontinuous elements include, but are not limited to, carbon fibers,glass fibers, aramid fibers, heating wires, sensing wires or acombination of multiple of these. For purposes of this disclosure, theseare referred to as continuous elements and the phase containing thecontinuous elements is termed CMC (Continuous Multifunctional Composite)phase. Further, continuous elements are not limited to function asstructural, sensing, heating or cooling elements. The polymericmaterials that can be used in each phase includes, but is not limitedto, thermoplastics, thermosets or elastomers. It should be noted thatthe word “phase” in the context of this document is used to refer to oneof the multiple material forms utilized in the co-extrusion additivemanufacturing process disclosed herein, rather than to the individualconstituents of such a material form.

The wide range of possible combinations of continuous elements within asingle phase led to the creation of the concept of ContinuousMultifunctional Composite (CMC) to refer to the phase of continuouselements fully impregnated with a polymeric material. The phrase “firstphase” refers to the phase containing molten material that isco-extruded with the CMC phase. The phrase “second phase” is used in thecontext of this disclosure to refer to continuous elements contained ina polymeric matrix and is analogous to the CMC. It should be recognizedthat the concepts and methods and apparatus of this disclosure are notlimited to printing with two phases only. Those skilled in the art willrecognize that the concepts of the methods and the apparatus of thisdisclosure can be extended to include printing with more than two phasesor just one phase.

In one embodiment of the methods of this disclosure, additivemanufacturing of an article containing CMC involves the following steps.First, feeding the CMC from a storage container or spool into aco-extrusion nozzle. Second, cutting the CMC to a predefined length toallow selective placement of CMC within an additively manufacturedarticle. Third, co-extruding the CMC with a phase containing moltenpolymer to provide thermal energy for melting the polymer in the CMC.Fourth, depositing the coextruded material system on a surface.

The method for printing with continuous elements disclosed hereinovercomes three primary limitations found in prior-art related tofilament-based methods for printing with continuous elements. Theseprior art methods are described in U.S. Pat. No. 9,126,365 B1 titled“Methods for composite filament fabrication in three dimensionalprinting” issued to Mark et al. on Sep. 8, 2015. Additional prior artrelated to printing with continuous fibers is described in U.S. Pat. No.9,511,543 B2 titled “Methods and apparatus for continuous compositethree-dimensional printing” and issued to Tyler on Dec. 6, 2016. Thecontents of these prior art patents mentioned above are incorporated byreference in their entirety into this disclosure. These prior-artfilament-based methods only allow printing with filament feedstockmaterials and are referred to as fused filament fabrication or fuseddeposition modeling. In these methods, melting of the polymeric materialis achieved only through thermal diffusion from the extrusion nozzle tothe filament. Therefore, the limitations include, 1) the incompleteimpregnation of continuous elements with polymer inside a phase as wellas the incomplete impregnation of this phase with the surroundingphases; 2) the limited deposition rate controlled by the time necessaryto diffuse thermal energy from an extrusion nozzle to a filamentcontaining continuous elements. Thermal diffusion is required to meltthe polymer matrix in the filament and thus to allow pressure flow ofthe material through the orifice of the extrusion nozzle; and 3) theneed for interrupting the printing process to deposit filament withcontinuous elements during the AM process of an article.

Printing with multi-phase materials can be accomplished by aco-extrusion process where the CMC is fed into a co-extrusion nozzleconveying a phase with molten material. The molten phase can be either areinforced or non-reinforced thermoplastic, thermoset or elastomer. Asthe CMC enters the co-extrusion nozzle, the CMC is combined with moltenpolymeric material. The molten polymer material can be supplied by asingle-screw extruder or by an extrusion melt pump. In these cases thephase in the molten state can result from the extrusion of a pelletizedfeedstock material. The pressure built inside the nozzle enhanceswetting of the surface of the CMC with the molten polymer, therebyreducing the thermal resistance to diffuse thermal energy from themolten phase into the second or multiple phases. Clearly, thermaldiffusion is driven by the temperature difference between the phase withmolten material and the CMC phase, which enters the nozzle in the solidstate. Additional thermal energy is supplied to the multi-phase materialsystem from the surface of the flow pathway in the co-extrusion nozzle.The diffusion of sufficient thermal energy for melting the polymer inthe CMC phase involves a characteristic time that depends on thediameter and initial temperature of the CMC phase. Further, themulti-phase material system flows at a given velocity through the flowpathway in the co-extrusion nozzle, thereby giving rise to a minimumco-extrusion distance required for melting the polymer in the CMC phase.

A CMC phase containing continuous elements with high elastic modulus canonly experience a small bending radius in the solid state beforedamaging the CMC. To prevent this condition, the polymeric material inthe CMC must be in the molten state to allow relative displacement ofthe continuous elements and thereby allowing bending of the CMC in asmall radius. An example of a small bending radius developed during theadditive manufacturing process of an article occurs as the coextrudedmaterial turns from the co-extrusion direction (nozzle direction) to thedeposition direction (perpendicular to the nozzle direction). In thecase that the polymeric material in the CMC remains is the solid state,excessive stresses can develop in the CMC, thereby causing the ruptureof continuous elements.

Designing a nozzle that ensures melting of the polymer in the CMC phaseat the end of the nozzle involved performing a transient heat transferanalysis for predicting the temperature evolution in the phases flowingthrough the co-extrusion nozzle. The following heat equation was derivedby carrying out an energy balance around an infinitesimal elementconsidered inside the co-extrusion nozzle. To capture the energyconveyed with the fluid flow, the advection term,

${\rho\; C_{p}v_{z}\frac{\partial T}{\partial z}},$was included in the heat equation. The velocity of the flow v_(z)represents the co-extrusion speed defined in the Z direction in aCartesian coordinate system. The density p and the heat capacity C_(p)are also in the advection term.

$\begin{matrix}{{{\frac{\partial}{\partial x}\left( {k_{x}\frac{\partial T}{\partial x}} \right)} + {\frac{\partial}{\partial y}\left( {k_{y}\frac{\partial T}{\partial y}} \right)} + {\frac{\partial}{\partial z}\left( {k_{z}\frac{\partial T}{\partial z}} \right)} - {\rho\; C_{p}v_{z}\frac{\partial T}{\partial z}} + \overset{.}{q}} = {\rho\; C_{p}\frac{\partial T}{\partial t}}} & (1)\end{matrix}$Orthotropic thermal diffusion is described through the three thermalconductivities k_(i), i=x, y, z. In addition to the diffusion andadvection terms, an external heat source {dot over (q)} is included toaccount for the latent heat associated with phase change. For the caseof the material considered in the investigations that led to thisdisclosure, this term captures the thermal energy that is eitherabsorbed in the event of melting of polymer crystals or released in theevent of polymer crystallization. The polymeric material considered inthe CMC phase consists of a semi-crystalline polymer, namelyPolyphenylene Sulfide (PPS). The boundary conditions for crystallinityconsidered at the inlet of the co-extrusion nozzle for the CMC phase andthe molten phase were fully crystallized (e.g. X_(vc)=X_(vc∞)) and fullymolten (e.g. X_(vc=0)), respectively. Two models, one describing polymercrystallization and other describing polymer melting, were used todescribe the evolution of crystallinity in the domain of the multiphasematerial system. The crystallization process is temperature and timedependent and thus the model proposed in literature by Velisaris andSeferis was used. This model describes the evolution of crystallinity asa function of two mechanisms described by integral expressions F_(vc)_(i) , i=1, 2 and weighted through the weighting factors w_(i), i=1, 2.The maximum fraction of crystallinity X_(vc∞) multiplies the sum of thetwo weighted integral expressions that vary from zero to one to definethe degree of crystallinity.X _(vc)(T,t)=X _(vc∞)(w ₁ F _(vc) ₁ +w ₂ F _(vc) ₂ )  (2)Similarly, the melting process of the crystalline regions in the polymerare described using the model developed by Greco and Maffezzoli andreported in literature. This model assumes a statistical distribution ofpolymer crystal lamellar thickness and thus the melting process is onlytemperature dependent.

$\begin{matrix}{\frac{{dX}_{vc}}{dT} = {k_{mb}{\left\{ {\exp\left\lbrack {- {k_{mb}\left( {T - T_{c}} \right)}} \right\rbrack} \right\} \cdot \left( {1 + {\left( {d - 1} \right){\exp\left\lbrack {- {k_{mb}\left( {T - T_{c}} \right)}} \right\rbrack}}} \right)^{\frac{d}{1 - d}}}}} & (3)\end{matrix}$

where k_(mb) and d capture the sharpness and the shape factor of thedistribution of lamellar thickness, respectively. T_(c) Is thetemperature recorded at the energy peak of the exothermic reactionrecorded in DSC experiments. Due to the consistent distribution ofcrystal lamellar thickness formed at different cooling rates, thetransition between the crystallization and melting models is defined bythe following temperature condition.

$\begin{matrix}{{X_{vc}(T)} = \left\{ {{\begin{matrix}{{T > T_{m}^{*}},} & \left. {{X_{vc}(T)} - {Melting}}\rightarrow{{Equation}\mspace{14mu} 3} \right. \\{{T \leq T_{m}^{*}},} & \left. {{X_{vc}(T)} - {Cyrstallization}}\rightarrow{{Equation}\mspace{14mu} 2} \right.\end{matrix}X_{vc}} \in \begin{bmatrix}0 & 1\end{bmatrix}} \right.} & (4)\end{matrix}$

where T_(m)* is the temperature at the onset of melting Similar to theheat transfer analysis, the effect of the material flow must beconsidered in the evolution of crystallinity during the co-extrusionprocess. Therefore, the material derivative of the degree ofcrystallinity is carried out and rearrange as given by Equation 5 todescribe the evolution of the crystallinity in an Eulerian frame ofreference.

$\begin{matrix}{\frac{\partial X_{vc}}{\partial t} = {\frac{{DX}_{vc}}{Dt} - {\frac{\partial X_{vc}}{\partial z}v_{z}}}} & (5)\end{matrix}$

The analysis described above was implemented in a UMATHT user subroutineand solved numerically using the commercial finite element packageABAQUS® known in the literature. Initial conditions for crystallinityand temperature were imposed in the heat transfer analysis as well asthe respective temperature boundary conditions at the inlet and body ofthe nozzle. Initial and boundary conditions at the inlet of theco-extrusion nozzle for the CMC were assumed at constant roomtemperature. Similarly, the PPS processing temperature (300° C.) wasused for the initial and boundary conditions at the inlet of theco-extrusion nozzle of the second phase since this enters theco-extrusion nozzle while is molten. A constant temperature boundarycondition was imposed on the wall of the co-extrusion nozzle. The twophases considered in this analysis include a CMC phase containing PPSreinforced with 40% by volume of carbon fiber and a molten phasecontaining PPS reinforced with 50% by weight of discontinuous carbonfiber. The material properties utilized in the heat transfer analysiswere predicted utilizing micromechanics methods and characterizedexperimentally for the continuous and discontinuous phases,respectively.

The heat transfer, polymer melting and polymer crystallization analysisprovided predictions of the temperature and crystallinity distributionsin the multiphase material during the co-extrusion process. Referring tothe top section in FIG. 1, a cross-sectional view of the co-extrusionnozzle shows an schematic representation of the multiphase materialsystem containing a CMC phase (dark) and a molten phase (grey), thesecond section from the top in FIG. 1 shows the steady state temperaturedistribution developed in the multiphase material system for theco-extrusion speed of 3500 mm/min.; the third section from the top inFIG. 1, shows the steady state temperature distribution developed in themultiphase material system for the co-extrusion speed of 2000 mm/min;and, the fourth section from the top in FIG. 1 shows the steady statetemperature distribution developed in the multiphase material system forthe co-extrusion speed of 1000 mm/min.

The degree of crystallinity in the multiphase material system alsochanged as a function of the co-extrusion speed. FIG. 2 shows at the topsection, a cross-sectional view of the co-extrusion nozzle. In thissection, the CMC phase is shown in black whereas the molten phase isshown in grey. Referring to the same FIG. 2, the second section from thetop shows the steady state distribution of crystallinity developed inthe multiphase material for the co-extrusion speed of 3500 mm/min.; thethird section from the top shows the steady state distribution ofcrystallinity developed in the multiphase material for the co-extrusionspeed of 2000 mm/min.; the fourth section from the top shows the steadystate distribution of crystallinity developed in the multiphase materialfor the co-extrusion speed of 1000 mm/min. Referring to the secondthrough the fourth regions from the top in FIG. 2, the light greyregions correspond to material that is in the molten state (amorphouspolymer) whereas the dark regions indicate material that is in the solidstate (crystalline polymer). FIG. 2 also shows the dependence of theco-extrusion speed on the position of the melt front along the length ofthe co-extrusion nozzle. While a co-extrusion speed of 1000 mm/mincauses the location of the melting front closer to the inlet of the CMCphase, a co-extrusion speed of 3500 mm/min moves the melting front to alocation closer to the outlet of the co-extrusion nozzle.

The process for designing the co-extrusion nozzle required first todefine a target volume fraction of CMC for the co-extruded bead. Atarget volume fraction of 10% of CMC phase was chosen to demonstratethis technology. Considering the average diameter of an existing CMCphase (1.26 mm), a nozzle diameter of 4 mm was determined to fulfill therequired volume fraction. A maximum extrusion speed of 3500 mm/min wasdetermined based on the nozzle diameter and a throughput of 10 lb/hourgiven by an existing extrusion system. Upon defining these processingconditions, heat transfer analyses were performed with different nozzlelengths to determine a minimum length that ensures the polymer in theCMC phase is molten at the end of the nozzle. A nozzle length of 70 mmwas found after multiple investigations. However, the length of thenozzle was extended by 2.5 mm due to geometric constraints imposed bythe existing EDAM system and therefore the final nozzle lengthconsidered was 72.5 mm.

In experiments leading to this disclosure, in order to integrate the CMCphase in an existing EDAM process, a system that embodies a customdesigned co-extrusion nozzle, a custom developed control algorithm, anda custom developed feeding mechanism were developed. The integration ofthis system in commercial EDAM machines enables selectively printing amaterial system containing at least two phases without interrupting theprinting process. This is achieved by co-extruding multiple phases ofmaterial through the co-extrusion nozzle. During the printing processwith multiple phases, the co-extrusion nozzle is actively heated and fedwith at least one of the polymer phases in the molten state. A second oreven multiple other phases enter the co-extrusion nozzle and merge withthe flow of the molten phase. Co-extruding multiple phases have at leasttwo advantages that differentiate this technique from existing systemsfor printing with continuous fiber systems. First, multiple phases inthe solid state can be heated and melted as these are conveyed alongwith the phase in the molten state in the co-extrusion nozzle, therebyallowing deposition of multiphase material systems at higher rates.Second, the pressure developed inside the co-extrusion nozzle enhancesthe wetting of the solid phases with the phases in the molten state,which improves the thermal diffusion from the molten phase into thesolid phases. The enhanced wetting achieved with this method alsoimproves the bonding between different phases and the load transferbetween the multiple phases.

The co-extrusion system or apparatus developed for printing withmultiple phases was designed as a supplementary component that can beintegrated in existing EDAM systems by replacing the regular extrusionnozzle with this co-extrusion system. FIG. 3 shows the co-extrusionsystem disclosed herein for printing with two phases, a CMC phase and aphase with molten polymer). FIG. 3 shows a schematic representation ofthe co-extrusion nozzle with the three primary components of aco-extrusion system: 1) The feeding system, 2) the cutting system and 3)the co-extrusion nozzle. A more detailed description of the threecomponents in given below.

First, the feeding system contains one or multiple pairs of rollers thatfunction as conveyors for the CMC phase. The rollers are designed toaccommodate CMC elements with a wide variety of diameters and shapes.The rollers can be driven by any type of electric motor. Further, aconstant pressure is maintained between each pair of rollers to maintaincontact between the CMC and the rollers and to improve traction.

Second, the cutting system (see FIG. 3) contains a blade that is pressedagainst the CMC phase when cutting, thereby enabling to cut the CMCphase at any time during the printing process. This way, the CMC phasecan be cut at predefined lengths and printed selectively. The cuttingblade can be actuated via electric, pneumatic, hydraulic, or other typeof mechanisms.

Third, the co-extrusion nozzle (see FIG. 3) combines CMC phase with thephase in the molten state. The phase in the molten state consist of areinforced or non-reinforced polymer composite. The CMC phase and thephase in the molten state are pressurized, driven out of theco-extrusion nozzle, and deposited. The CMC phase is guided to enter theco-extrusion nozzle tangent to the flow of molten material. However, thefeeding system can be oriented at any angle with respect to theco-extrusion nozzle. This design permits easy alignment of the CMC phasewith the incoming material and prevents sharp bending of the CMC whichcould cause its rupture.

FIG. 4A shows a cross-sectional view of the co-extrusion apparatus 4000of this disclosure with detail of several of its constituent parts.Referring to FIG. 4A, CMC phase 4100 is stored in reels (not shown) thatfeed the feeding system 4200 of the co-extrusion apparatus 4000 with acontinuous element of CMC phase 4100. The first point of contact betweenthe co-extrusion apparatus 4000 and the CMC phase 4100 is the feedingsystem 4200. A non-limiting example of a feeding system contains a setof pinch rollers 4210 that compress and propel the CMC phase 4100 fromthe reels and into the feeding channel 4300. A constant pressure isapplied across the pinch rollers 4210 through an adjustable springloaded mechanism 4220. A non-limiting example of a cutting mechanism4400 to size the CMC phase 4100 to the desired length is also shown inFIG. 4A. The cutting mechanisms 4400 contains a shear cutter 4410actuated with a pneumatic piston (not shown) that trims the CMC phase4100. The feeding channel 4300 guides the CMC phase 4100 to theco-extrusion nozzle 4500. The feeding of CMC phase 4100 into theco-extrusion nozzle 4500 can be at any desired angle. This angle can beselected for either ease entry of the CMC phase 4100 into theco-extrusion nozzle 4500 or based on the minimum allowable bendingradius of the CMC phase 4100. A non-limiting example of a co-extrusionnozzle 4500 is shown in FIG. 4A. The co-extrusion nozzle 4500 contains aport 4510 for a pressure sensor (not shown) and a port 4520 for atemperature sensor (not shown). The CMC 4100 merges into the flow streamof the molten material 4600 entering the extrusion nozzle 4500. The CMCphase 4100 is combined with the phase in the molten state 4600 insidethe flow pathway 4530 of the co-extrusion nozzle 4500. The co-extrusionnozzle 4500 contains the nozzle tip 4540 to allow changes in thedimensions and geometry of the flow pathway 4530. The extrudate 4700emerging from the nozzle tip 4540 contains a multiphase material thatflows through the flow pathway 4530 and emerges from the nozzle tip4540. Clearly, the extrudate 4700 contains the CMC phase 4100 and thephase provided in the molten state 4600. It should be recognized thatthe nozzle tip 4540 can be changed as desired to meet the requirementsof the geometry and dimensions of the extrudate 4700.

FIG. 4B shows a simplified cross-sectional view of the co-extrusionsystem or apparatus of this disclosure, showing the trajectory the CMCfollows from the feeding system until the end of the co-extrusionnozzle.

Co-extruding technology has been in industry for a long time, however,the existing control systems are not suitable for utilizing thistechnology in the context of additive manufacturing. As a result, anovel control approach for continuously and selectively dispensing a CMCphase was developed and described in this disclosure. Further, thiscontrol approach can be readily extended to accommodate feeding multiplephases simultaneously. The structure of the control system is summarizedas follows.

To start printing with CMC, an event either included in the machine codeused for commanding an EDAM system or manually introduced by the usertriggers the multiphase co-extrusion system. Upon this triggering, thefeeder is the first component that is activated. At the same time, thecontrol system determines through an algorithm the appropriate timingand speed required to deliver the CMC phase at the desired time andposition in the printing process. The distance between the feedingsystem and the end of the co-extrusion nozzle is considered in thecalculations of timing and feeding speeds. For the event of disablingthe co-extrusion process during the printing process of an article, thecontrol system calculates the appropriate time to stop feeding the CMCphase into the co-extrusion nozzle and triggers the cutting system. Itshould be mentioned that process conditions such as differentco-extrusion speeds between the CMC phase and the phase in the moltenstate are possible with the control system.

In experiments leading to this disclosure, a polymer impregnationprocess for continuous elements described in U.S. Pat. No. 4,783,349titled “Process for making fiber reinforced products “issued to Cogswellet al. on Nov. 8, 1988 was utilized to produce the CMC phase. Thecontents of this patent are incorporated by reference in their entiretyinto this disclosure. The impregnation process by pultrusion describedin this patent was utilized to create the CMC phase containingcontinuous elements and a polymeric material. The continuous elementsthat can be used in a CMC phase include, but are not limited to, carbonfibers, glass fibers, metallic fibers, sensing elements, electronicelements or a combination of two or more of these elements listed. Thepolymeric materials that can be utilized to impregnate the continuouselements include, but are not limited to, thermosetting polymers,thermoplastic polymers or elastomers.

In addition to reinforcing printed composites, applications that willleverage the versatility of the CMC include, but are not limited toarticles reinforced with CMC containing reinforcing fibers and sensorsfor applications of structural health monitoring in sectors such asautomotive, aerospace or sporting equipment. In addition to theinclusion of this technology on existing products, the tooling industrywhich is undergoing a revolution with the arrival of the additivemanufacturing technologies could leverage other features of the CMC likeactive heating or cooling in tools for compression molding, injectionmolding, resin transfer molding or any other polymer or compositeprocessing tool.

FIG. 5 shows a computer aided design (CAD) representation of a mold thatis capable of being additively manufactured wherein selective layers cancontain multiphase materials incorporated utilizing the methods andapparatus of this disclosure.

FIG. 6 shows a schematic representation of a cross-section of anadditively manufactured mold containing a multiphase material shown as6100. The detailed view included in FIG. 6 shows an extrudate ofmultiphase materials 6100 also referred to as printed bead or unit cell6100. The extruded bead 6100 contains the CMC phase 6200, which issurrounded by the phase 6300 which can contain a polymer anddiscontinuous elements. The phase 6300 results from the solidificationof the phase in the molten state 4600 shown in FIG. 4A.

FIG. 7A shows an exemplary microstructure of the CMC phase 6200 shown inFIG. 6. FIG. 7B shows enlarged view of the area designated by white dotsin FIG. 7A. Referring to the microstructure of the CMC phase shown inFIG. 7B, the carbon fibers are shown as white circles and are enclosedin the polymer matrix shown in grey, which is a direct representation ofthe high level of impregnation achieved with the pultrusion process.Hence, the deficient fiber impregnation attained with existingtechnologies for printing with continuous fibers is mitigated byco-extruding a CMC phase fabricated by pultrusion.

Multiple benefits and a wide range of new possibilities are readilyrecognized by printing CMCs with the apparatus and methods of thisdisclosure. However, the benefit of printing with CMCs specificallydesigned for improving the mechanical properties, namely stiffness andstrength, has been investigated through analytical tools. It should benoted that a structural CMC has been already produced with carbon fiberand PPS through an existing pultrusion process. An engineering analysisusing micromechanics was carried out to determine the improvement instiffness achieved by combining the structural CMC phase with a phasecontaining PPS reinforced with 50% by weight of discontinuous carbonfiber.

The elastic modulus of the composite is greatly influenced by the fibervolume fraction whereas the strength of the composite is greatlyinfluenced by the fiber length. As a result, the contribution of thestructural CMC phase to the strength of the printed materials isexpected to be more significant than the increase in elastic modulus.Predicting strength requires further understanding of the microstructuredeveloped during in the co-extrusion process with CMC as well as thefailure mechanisms governing the strength of the composite, thereforepredictions are limited to stiffness thus far.

The finite element method was used to conduct a micromechanical analysisof a mesostructure containing three constituents as shown in therepresentative volume element (RVE) depicted in FIG. 8. The constituentshown in dark-grey correspond to discontinuous fibers in the moltenphase used in the co-extrusion process, whereas the constituent inlight-grey corresponds to continuous fibers in the CMC. The thirdconstituent shown in white corresponds to the polymer. The followingassumptions were made for the sake of this initial predictions of theelastic modulus: continuous fibers are assumed to be dispersed acrossthe RVE while the orientation was enforced in the print direction; thematrix is assumed to be isotropic and the fibers transversely isotropic.Further, both materials are assumed to behave linearly elastic. Thefibers are assumed to be cylindrical with constant diameter and aperfectly bonded or non-slip condition is assumed at the fiber-matrixinterface. The orientation of the fibers in the phase with discontinuousfibers does not consider the effect that co-extruding the CMC could haveon the final fiber orientation.

Table 1 lists the properties of the constituent materials obtained fromthe literature cited in this disclosure and used in the prediction ofthe elastic modulus of the co-extruded material.

TABLE 1 Properties of constituent materials used in micromechanicsanalysis Polyphenylene Sulfide (PPS) E (GPa) 3.5 v 0.3 AS4 Carbon FiberE₁(GPa) 235.0 E₂ = E₃ (GPa) 14.0 v₁₂ = v₁₃ 0.2 v₂₃ 0.25 G₁₂ = G₁₃(GPa)28.0 G₂₃(GPa) 5.5

As mentioned before, a volume fraction of 10% of continuous phase waschosen as initial testing condition, which was also used for determiningthe critical nozzle length. The fiber volume fraction inside thecontinuous phase is 40% whereas the fiber volume fraction in the phasewith discontinuous fiber is 40%. Therefore, the fiber volume fraction of40% is preserved in the final co-extruded material. With regards to thefiber orientation, the second order orientation tensor known by thoseskilled in the art [A]_(cf) and [A]_(df) describes the orientation statein the phase with continuous and discontinuous fibers, respectively.

$\lbrack A\rbrack_{df} = {{\begin{bmatrix}0.8 & 0 & 0 \\0 & 0.15 & 0 \\0 & 0 & 0.05\end{bmatrix}\lbrack A\rbrack}_{cf} = \begin{bmatrix}1.0 & 0 & 0 \\0 & 0 & 0 \\0 & 0 & 0\end{bmatrix}}$The elastic modulus in the 1-direction predicted for the system ofdiscontinuous fiber and 10% of CMC and the discontinuous fiber system isreported in Table 2. The value for the discontinuous fiber system agreeswith experimental results obtained for the same material system whichprovides confidence in the predictions made through micromechanics forthe material system including CMC.

TABLE 2 Prediction of elastic moduli for material system reinforced withCMC and without CMC Property V_(df) = 100 V_(df) = 90, V_(cf) = 10E₁(GPa) 26.4 36.2

An improvement of around 37% in the elastic modulus (E₁) can be gainedby inserting 10% of CMC in the carbon fiber reinforced PPS used forprinting. Furthermore, a significant improvement in the strength of theprinted composite is expected for the material system including CMCs.These two significant improvements in the mechanical properties ofprinted composites can enable printing structural components that onlyrequired in-plane properties. Nevertheless, this system or apparatus forprinting CMC can be readily extended for 3-D printing with multipleaxes.

Both the CMC and the apparatus or system for printing with multiplephases were described in this disclosure. A heat transfer analysis ofthe co-extrusion process was carried out to determine processingconditions needed to melt the polymer in the CMC

phase. The results from the heat transfer analysis were used to guidethe design process of the co-extrusion nozzle disclosed herein. Acontrol scheme developed for printing with continuous fibers wasoutlined. Results obtained through micromechanical analysis of thetarget mesostructure revealed the improvements gained in stiffness dueto the addition of continuous fibers.

Tooling, molds, jigs and fixtures used in autoclave and compressionmolding composites manufacturing are examples of articles produced withthe methods and apparatus for co-extruding CMC in the EDAM process.

Based on the above description, it is an objective of this disclosure todescribe method of depositing a multiphase material. The method includesproviding a CMC phase containing at least one continuous elementcontaining at least one material impregnated in a polymeric matrix;passing the CMC phase containing the at least one continuous elementthrough a feeding system containing a cutting system; producing apredetermined length of the CMC phase containing at least one continuouselement by activating the cutting system; providing a flow a moltenpolymer such that the molten polymer and the CMC phase containing atleast one continuous element of predetermined length are merged into acontinuous co-extrusion nozzle so as to produce a co-extruded multiphasematerial; and depositing the co-extruded multiphase material onto asurface. The surface can be part of a substrate, a component or anarticle. The substrates can be made of metallic, ceramic, or organicmaterials, such as polymers. The components or articles on which theco-extruded multiphase material can be printed can include, but notlimited to articles or components which are additively manufactured ormanufactured by other processes.

Examples of at least one continuous element include, but is not limitedto, carbon fiber, glass fiber, jute fiber, and aramid fiber. In someembodiments of the method, at least one material can be a semiconductor,such as, but not limited to silicon or a material containing silicon. Insome embodiments of the method, at least one material can be a metallicmaterial, such as a metal or an alloy. Non-limiting examples of an alloysuitable for the purpose are Cr—Ni alloy, a Cr—Mo alloy and a Cu—Nialloy.

In some embodiments of the method described above, the molten polymercan be, but not limited to, a thermoplastic polymer, a thermosettingpolymer, or an elastomer. Examples of thermoplastic polymers suitablefor the purpose, include, but not limited to, Polyphenylene sulfide(PPS), polypropylene (PP), polyether ether ketone (PEEK) andacrylonitrile butadiene styrene (ABS). Examples of thermosettingpolymers suitable for the purposes of the method include, but notlimited to, an epoxy, a vinyl-ester and a polyester. Examples ofelastomers suitable for the method include, but not limited to, naturalrubber, polyurethane, polybutadiene, neoprene, and silicone.

In some embodiments of the method the molten polymer can be made frompellets using a single-screw extruder or an extrusion melt pump. Boththese methods are known to those of skilled in the art.

In some embodiments of the method, the molten polymer is reinforced withdiscontinuous fibers. Examples of such fibers include, but not limitedto carbon fibers, glass fibers, jute fibers, and aramid fibers. In someembodiments of the method, the surface is chosen to be detachable fromthe deposited material. In some embodiments of the method, the surfaceis a layer of a co-extruded multiphase material. In some embodiments ofthe method, polymeric matrix contains a thermoplastic resin or athermoplastic resin or both.

In some embodiments of the method, wherein the at least one material canbe more than one material. In such a case, for example, the materialscan contain a structural material and a sensing material. Examples ofstructural materials include, but not limited to a carbon fiber. Anon-limiting example of a sensing material is a Cu—Ni alloy wire capableof sensing strain. In some embodiments of the method the more than onematerial is a combination of a structural material and a heatingmaterial. A non-limiting example of a heating material is Ni—Cr alloy.

Those skilled din the art will readily recognize the above methods to besuitable for additive manufacturing of articles and components.

In some embodiments of the method, the at least one continuous elementcan be a plurality of continuous elements. In such a case, where themethod uses two or more continuous elements, different continuouselements can be utilized to achieve the same function or differentfunctions.

In some embodiments of the method, the surface on which the multiphasematerial can be can be a layer of a co-extruded multiphase material.This also means multiple layers of the multiphase material can bedeposited utilizing the methods of this disclosure.

It should be recognized that in the methods described above, onecontinuous element can contain one or more materials. The materials in acontinuous elements can all have same function or different functions.

It can be seen from the above that a variety of functionalities for theprinted multiphase material or possible by judicious selection of thecontinuous elements and by the selection of materials used in thecontinuous elements.

It is another objective of this disclosure to describe an apparatus fordepositing a multiphase material. The apparatus includes a feedingssystem capable of continuously feeding a CMC phase containing continuouselements, and containing a cutting system capable of producing apredetermined length of the CMC phase containing continuous elements; aco-extrusion nozzle comprising a flow channel; a means to introduce thepredetermined length of the CMC phase containing continuous elementsinto the flow channel of the co-extrusion nozzle; and a means tointroduce a molten polymer into the flow channel such that the moltenpolymer and the predetermined length of the CMC phase containingcontinuous elements are co-extruded and deposited on a surface. Theapparatus can thus be used to produce an article or a component byadditive manufacturing.

It can be seen that the methods and apparatus disclosed can be can beutilized to produce an article or a component. It is also an objectiveof this disclosure to describe an article or component comprising a CMCphase containing continuous elements embedded in a polymer resin forminga multiphase structure. In some embodiments of the article, thecontinuous elements provide both mechanical strength and a sensingcapability. The continuous elements suitable for the CMC phase and thepolymer resin have been described above with reference to the methodsdetailed above for fabricating a component. The sensing capability canbe utilized to sense strain, temperature or pressure as non-limitingexamples. Examples of structural materials include, but not limited to,carbon fibers. A non-limiting example of a sensing material is a Cu—Nialloy wire capable of sensing strain. It should be recognized that insome embodiments of the articles of this disclosure different elementsof the CMC phase can perform different functions. For example an elementcan provide mechanical strength while a second element can be utilizedas a sensor for strain. It is to be recognized that in some embodiments,the same element embedded in the CMC phase can perform multiplefunctions.

The invention has been described in detail with particular reference tocertain preferred aspects thereof, but it will be understood thatvariations, combinations, and modifications can be effected by a personof ordinary skill in the art within the spirit and scope of theinvention. Other implementations may be possible.

The invention claimed is:
 1. A method of depositing a multiphase material, the method comprising: providing a CMC phase containing at least one continuous element comprising at least one material impregnated in a thermoplastic resin; passing the CMC phase containing the at least one continuous element through a feeding system containing a cutting system; producing a predetermined length of the CMC phase containing at least one continuous element by activating the cutting system; providing a flow a molten polymer comprising polyphenylene sulfide such that the molten polymer and the CMC phase containing at least one continuous element of predetermined length are merged into a continuous co-extrusion nozzle so as to produce a co-extruded multiphase material; and depositing the co-extruded multiphase material onto a surface.
 2. The method of claim 1, wherein the at least one material is one of carbon fiber, glass fiber, jute fiber, and aramid fiber.
 3. The method of claim 1, wherein the at least one material is a semiconductor material.
 4. The method of claim 3, wherein the semiconductor material comprises silicon.
 5. The method of claim 1, wherein the at least one material is a metallic material.
 6. The method of claim 5, wherein the metallic material is a metal or an alloy.
 7. The method of claim 6, wherein the alloy is one of a Cr—Ni alloy, a Cr—Mo alloy, and a Cu—Ni alloy.
 8. The method of claim 1, wherein the molten polymer is made from polymer pellets using a single-screw extruder or an extrusion melt pump.
 9. The method of claim 1, wherein the molten polymer is reinforced with discontinuous fibers.
 10. The method of claim 1, wherein the fibers are one of carbon fibers, glass fibers, jute fibers, and aramid fibers.
 11. The method of claim 1, wherein the surface is a layer of a co-extruded multiphase material.
 12. The method of claim 1, wherein the CMC further comprises a thermosetting resin.
 13. The method of claim 1, wherein the at least one material is more than one material.
 14. The method of claim 13, wherein the more than one material is a combination of a structural material and a sensing material.
 15. The method of claim 14, wherein the structural material is one of a carbon fiber.
 16. The method of claim 14, wherein the sensing material is Cu—Ni alloy wire capable of sensing strain.
 17. The method of claim 13, wherein the more than one material is a combination of a structural material and a heating material.
 18. The method of claim 17, wherein the structural material is carbon fiber and the heating material is Ni—Cr alloy.
 19. The method of claim 1, wherein the at least one continuous element is a plurality of continuous elements. 